This invention was made with Government support under Grant (Contract) No. DABT-63-95-C-0055 awarded by the Advanced Research Project Agency and Grant (Contract) No. ECS-9419112 awarded by the National Science Foundation. The Government has certain rights to this invention.
Optical scanners are used for scientific and industrial applications ranging from laser imaging and displays to laser surgery tools and home-office appliances, such as facsimile machines and printers. Barcode optical scanners are used for automatic object-identification. Most optical scanners use a polygon mirror. Unfortunately, a polygon mirror requires precision machining for the polygon surfaces to insure flatness and repeatability when the laser beam sweeps across the reflecting facets. In addition, a polygon mirror is relatively bulky. A polygon mirror can be considered a macroscopic device. As used herein, a macroscopic device is a device with a third dimension greater than approximately several milli-meters, where the third dimension refers to the height above a horizontal substrate. A microscopic device is a device with a third dimension less than approximately several milli-meters.
Silicon-surface-micromachining technology has been used to fabricate microscopic devices. In particular, optical microelectromechanical systems (MEMS) have been implemented with movable-micromirrors. FIG. 1 illustrates an optical MEMS 20 in accordance with the prior art. The optical MEMS 20 includes a MEMS mirror assembly 22, which optically links a laser 24 to an optical fiber 26. A lens assembly 28 is positioned between the laser 24 and the MEMS mirror assembly 22.
FIG. 2 is a more detailed illustration of a MEMS mirror assembly 22 that may be used with the apparatus of FIG. 1. The MEMS mirror assembly 22 includes a mirror 30 positioned on a mirror slider 32 through the use of hinges 34. Hinges 34 are also used to couple the top of the mirror 30 to the top of a support 36. The bottom of the support 36 is connected to a support slider 38 through the use of hinges 34.
The support slider 38 includes support slider comb fingers 40, which are in an inter-digit arrangement with stator comb fingers 42. The combination of the support slider comb fingers 40 and the stator comb fingers 42 form a comb drive 43. As known in the art, a comb drive uses capacitive charge between support slider comb fingers 40 and stator comb fingers 42 to alternately push the support slider 38 away from the stator comb fingers 42 or pull the support slider 38 toward the stator comb fingers 42. In this way, the mirror 30 can be fabricated within the horizontal plane of a semiconductor and then be lifted into a vertical configuration (third dimension) with respect to the semiconductor, as shown in FIG. 2. A comb drive may also be used in relation to the mirror slider 32 to facilitate this process.
FIG. 3 illustrates a pin-and-staple hinge 34, which includes a staple portion 35 and a pin portion 37. The pin portion 37 forms a segment of mirror 30. The figure illustrates how the mirror 30 is allowed to pivot about the hinge 34, thereby allowing the mirror 30 to be lifted from a horizontal plane of a semiconductor surface and into a vertical plane with respect to the semiconductor surface.
MEMS mirror assemblies of the prior art have been limited to relatively slow mirror movement. That is, the comb drives have been used to slightly modify an initial mirror position. Thus, MEMS mirror assemblies of the prior art have not been used for scanning. In other words, prior art MEMS mirror assemblies have not been used to rapidly traverse a range of positions in a coordinate axis. In the absence of this capability, the utility of MEMS in optical systems is limited. Accordingly, it would be highly desirable to provide a MEMS suitable for optical scanning operations. Such a device could thereby operate as a building block in a variety of opto-electrical equipment.